The present invention relates to a method for producing an optical article comprising a substrate provided with an antireflection coating or a reflective coating comprising a sub-layer, having in particular an increased abrasion-resistance and good adhesion properties to the substrate.
1. Field of the Invention
In the ophthalmic optics field, ophthalmic lenses are traditionally provided with various coatings so as to give these lenses a plurality of mechanical and/or optical properties. Successive coating layers are thus traditionally formed onto an ophthalmic lens, such as impact-resistant coating layers, abrasion-resistant coating layers, antireflection and/or reflective coating layers.
As defined hereunder, an antireflection coating means a coating that has been deposited onto the surface of an optical article, which does improve the antireflective properties of the optical end product. It makes it possible to reduce the light reflection at the article-air interface area within a relatively large portion of the visible light spectrum.
A reflective coating has the opposite effect, that is to say it does increase the light ray reflection. Such a coating type is used for example to provide sun lenses with a mirror effect.
2. Description of Related Art
Antireflection coatings are well known and do traditionally comprise a monolayered stack or a multilayered stack of dielectric materials such as SiO, SiO2, Al2O3, MgF2, LiF, Si3N4, TiO2, ZrO2, Nb2O5, Y2O3, HfO2, Sc2O3, Ta2O5, Pr2O3, or mixtures thereof.
As is also well known, antireflection coatings are preferably multilayered coatings comprising high refractive index layers and low refractive index layers, alternately.
Reflective coatings are made of layers that are the same in nature as for antireflection coatings, except that the refractive index values, the number and the thickness of the layers are chosen so as the coating to be reflective, which is well known to the one skilled in the art.
Even if the following description does refer to antireflection coatings it also applies to reflective coatings. However, the present invention preferably relates to antireflection coatings.
It is known to interleave a relatively thick sub-layer between the substrate and the high refractive index and the low refractive index layers of the antireflection coating so as to improve the abrasion-resistance and/or the scratch resistance of said coating.
However, it has been observed that inserting this sub-layer, while increasing the abrasion resistance properties, might weaken the antireflection stack and affect its adhesion to the substrate. Some defaults have been observed in particular at the sub-layer/antireflection optical stack interface.
The patent application WO 2005/059603, in the name of to the applicant, does describe an article comprising a coloured, multilayered antireflection coating comprising at least two high refractive index layers that do absorb in the visible range and that are based on substoechiometric titanium oxide TiOx (x<2) and preferably at least one low refractive index layer (LI) based on SiO2 doped with 1 to 5 weight % of Al2O3, as related to the total weight SiO2+Al2O3.
This document does more particularly describe a substrate successively coated with a 100 to 110 nm-thick silica sub-layer, a TiOx layer, a SiO2/Al2O3 layer, a TiOx layer, a SiO2/Al2O3 layer, a TiOx layer, a SiO2/Al2O3 layer and an anti-fouling coating.
Prior to depositing the antireflection coating, the substrate surface does undergo a treatment for increasing the sub-layer adhesion. This surface preparation, that is called IPC (ion Pre-cleaning), does consist of an ionic pre-cleaning by argon ion bombarding the substrate with an ion gun.
There is no surface treatment provided for the sub-layer.
The optical article produced according to the teaching of the patent application WO 2005/059603 does possess good adhesion and abrasion resistance properties that might nevertheless be improved.